ISSN:2149-455X 1 Review Article / Derleme

The Importance of The and Its Variations

Hüseyin Baylan

Sakarya Üniversitesi Tıp Fakültesi Anatomi Anabilim Dalı, Sakarya

Özet

Rutin osteoloji uygulamasında varyasyonel bir atlas karşımıza çıkabilir çünkü atlas omuru insandaki en çok varyasyona sahip omurdur. Boyna yapılan cerrahi operasyonlarda özellikle atlas omurunun varyasyonları cerrahlar tarafından önceden bilinmelidir çünkü atlas omuru ile çok yakın seyreden arteria vertebralis’lerin hasarlanması önlenmelidir. Arteria vertebralis’lerin meninksleri, dura mater’i, omuriliğin boyun kısmını ve spinal gangliyonları kanlandırmasından dolayı bu arterin hasarı vertebrobasiler iskemiye bağlı migren, vertigo, diplopia gibi durumlara yol açabilir. Vertebral venler ve arterin etrafındaki sinir pleksusu da atlasın travmalarında incinip klinik semptom ve komplikasyonları zenginleştirebilir. Anahtar Kelimeler: atlas vertebra, processus transversus, varyasyon, boyun omuru

Abstract

During routine osteology demonstration one may notice a variational atlas vertebra because the atlas is the most variable vertebra in man. The variations of it should be known especially before the operations to the performed by the surgeons because the vertebral arteries are close to it. And the vertebrobasilar ischemia which may lead to some bad conditions like migraine, vertigo, diplopia can be due to injuries of the vertebral arteries which supply blood to the meninges, dura mater, cervical part of the and spinal ganglions. The vertebral veins and the nervous plexus around the artery may also be injured in traumas of this region so these structures involved may enrich the clinical symptoms and complications. Keywords atlas vertebra, transverse process, variation, cervical vertebra

Corr. Author: Hüseyin Baylan Sakarya Üniversitesi Tıp Fakültesi Anatomi Anabilim Dalı, Sakarya review article E-mail: [email protected] 1 135 J hum rhythm - December 2016;2(4):134-137 Review Article / Derleme

Introduction behind the foramen. The first cervical vertebra, namely the atlas, supports the and is not a typical vertebra due to its shape and having neit- The foramen transversarium is limited by the “costotransverse her body nor spinous process (Figure1). bar” laterally which is grooved superiorly for the cervical spinal nerves crossing the vertebral vessels posteriorly 2.

At the superior aspect behind the lateral mass, the posterior arch has a groove for , venous plexus and dor- sal rami of first cervical nerve 3. The posterior atlantooccipital membrane attaches to the posterior arch of the atlas and at each lateral border the vertebral artery and the first cervical nerve pierce it 3.

In textbooks, atlantal width is between 74 mm and 95 mm in males and between 65 mm and 76 mm in females 1. However, the distance between tips of the transverse processes of the atlas ranged from 29.8 to 84.9 mm (mean 74.6 mm) in an article 4.

The vertebral artery is very crucial for neurology because it supplies the meninges, dura mater in the posterior cranial fos- sa, cervical part of the spinal cord and spinal ganglions 5,6. Exiting from the transverse foramen of the atlas, the vertebral A short anterior and a long posterior arches are joined with artery directs to a groove for itself at the posterior arch of the two thick lateral masses in the atlas anterolaterally. In the atlas behind the superior facet, then it enters the occipital midline of the atlas, both arches have a tuberculum at outer triangle and subsequently passes through the opening of the edges in the anteroposterior directions. The lateral masses ar- posterior atlantooccipital membrane to enter the cranial ca- ticulate with occipital superiorly, and with the supe- vity through 3,5,7. After entering foramen rior articular facet of the inferiorly. There is also a synovial magnum the two corresponding vertebral arteries converge joint for the dens of the axis at the inner face of the anterior to form the basilar artery 1. arch of the atlas to provide the position of the atlas with the help of the transverse ligament 1. A usual atlas has transver- There are some crucially important anatomical structures aro- se processes bilaterally with foramina transversarium. Among und the transverse processes of the atlas. For instance, the upper six , the atlas has the longest trans- styloid process is anterior to the transverse process and bet- verse processes that are useful for fine balancing of the head ween these two processes are the last three cranial nerves (X, movements thanks to some muscles inserted to the atlas 1. XI, and XII) and the internal jugular vein. The , the posterior belly of the digastric muscle and the stylohyoid The transverse process consists of anterior and posterior parts muscle are all lateral to the transverse process of atlas. Lastly, that form the foramina transversarium where the vertebral the is posterior to the transverse pro- vessels and nervous plexus are transmitted 2. The anterior part cess1,8. is called costal element or costal process because it is believed to be the homologue of the 1. The posterior part is direc- Above the posterior arch of the atlas, small vessels from inter- ted forwards and laterally and it is the true transverse process nal vertebral plexuses leave the vertebral canal and join with Review Article / Derleme J hum rhythm - December 2016;2(4):134-137 136

small veins in the suboccipital triangle to form a venous plexus cervical operations 12. Injuries of the vertebral artery may af- that enters the transverse foramen of the atlas around the fect the brain stem and cerebellum resulting in neurological vertebral artery. This venous plexus descending ends as the problems like unconsciousness, respiratory and cardiovascu- vertebral vein 1. lar impairments 4. A compression on the vertebral artery may cause vertebrobasilar ischemia which may lead to common Human atlas morphology correlates with head and neck pos- symptoms like migraine, vertigo, diplopia, shoulder pain, neck ture 9. The most variable vertebra in man is the atlas and the pain or severe incidents of cerebrovascular incidents 24. For- aetiological factors of these variations were explained on an tunately, in surgical operations, iatrogenic injury of the ver- embryological basis 10,11. tebral artery is reported to be rare 25. Besides in atlantoaxial region there are lots of surgical procedures like the interlami- The common variations of atlas reported in literature inclu- nar clamp and hook plating, lateral screw, and plate fixation, de incomplete unilateral or bilateral foramen transversarium and interspinous wiring being used in order to treat cervical 1,12,13, complete or incomplete retroarticular foramen (has lots instability 4. Atlas development is reported to be a factor in of synonyms 14), double foramina (or accessory transverse fo- some situations such as transient vertebrobasilar insufficiency, ramina) 6, abnormal foramina on posterior arch, incomplete Barre-Lieou syndrome, and chronic upper cervical syndrome posterior arch (split posterior arch), split anterior arch, spur 26. An article highlights that cerebellar haemorrhage compli- on anterior arch, a thick body, a thin vertebral artery groove, cations in supratentorial craniotomy operations may be due to abnormal inferior articular facet 3, split superior articular pro- the obstruction of the flow in the internal jugular vein which cess, different shapes of superior articular facet ( oval, 8-sha- sits anteriorly to the transverse process of the atlas 8. pe, kidney shape, bilobed, trilobed and irregular, triangular, V- shape and leaf shape 3), partial or total fusion of atlas with As a conclusion, an incomplete transverse foramen may be the occipital 15, and some accessory bony arches emb- confused radiologically with acquired anomalies when interp- racing the vertebral artery 10,16. Some accessory foramina may reting about X-ray and CT scans. Because of the crucial ne- be encountered in the atlas 17. ighbourhoods, the variations of the foramina transversarium should be well known before planning head and neck ope- Variations in the course of the vertebral artery are postula- rations by disciplines like neurosurgery, orthopaedic surgery ted to be the cause of variant foramina transversarium but to prevent especially vertebral artery injuries in order not to not well known 2,6,18. The vertebral artery occupies more than cause any neurological deficits. half of the diameter of the transverse foramen 5,6. As a result, the vertebral artery may be a factor to change the size of the transverse foramina formation due to tortuosity and bone erosion 19.

Atlas injuries are reported as 25% of all injuries to the atlan- toaxial complex 20. But the transverse process fractures are reported as rare 21. The fractures of the transverse process may injure vertebral arteries resulting in subarachnoid hae- morrhages 22. Especially in the neck operations, the transverse process of the atlas is told as an important landmark by sur- geons 23. When planning the operations to the neck region the vertebral artery injuries should be avoided by surgeons. Especially the incomplete foramen transversarium makes the second part of the vertebral artery vulnerable in posterior 137 J hum rhythm - December 2016;2(4):134-137 Derleme / Review Article

References

1. Susan Standring, Gray's anatomy: the anatomical basis of clinical practice. and William M Clark, Skeletal Radiology 1 (2), 97 (1976). (Elsevier Health Sciences, 2015). 22. CP Johnson, T How, M Scraggs, CR West, and J Burns, Forensic science 2. C Taitz, H Nathan, and B Arensburg, Journal of Neurology, Neurosurgery & international 109 (3), 169 (2000). Psychiatry 41 (2), 170 (1978). 23. Tzung-Shiahn Sheen, K Lawrence Yen, Jenq-Yuh Ko, and Mow-Ming Hsu, 3. C Gupta, P Radhakrishnan, Vikram Palimar, Antony Sylvan D’souza, and NL Otolaryngology-Head and Neck Surgery 122 (2), 284 (2000). Kiruba, J Morphol Sci 30 (2), 77 (2013). 24. A Krishnamurthy, SR Nayak, S Khan, Latha V Prabhu, Lakshmi A Ramanathan, 4. GOKSIN Sengul and HH Kadiaglu, Turkish neurosurgery 16 (2), 69 (2006). C Ganesh Kumar, and A Prasad Sinha, Rom J Morphol Embryol 48 (3), 263 5. Tarik H Abd El-Bary, Manuel Dujovny, and James I Ausman, Surgical (2007); Ahmet Kavakli, Atif Aydinlioglu, Hakki Yesilyurt, Ilter Kus, Semih neurology 44 (4), 392 (1995). Diyarbakirli, Saadet Erdem, and Omer Anlar, Saudi medical journal 25 (3), 6. Paul Bundi Karau and Paul Odula, Anatomy Journal of Africa 2 (1), 61 322 (2004). (2013). 25. Nabil A Ebraheim, Rongming Xu, Muhammad Ahmad, and Bruce Heck, 7. Bernard George and Jan Cornelius, Operative techniques in Neurosurgery Spine 23 (3), 320 (1998) 4 (4), 168 (2001); Arnold H Menezes and Vincent C Traynelis, Child's 26. M Buna, W Coghlan, M deGruchy, D Williams, and O Zmiywsky, Journal Nervous System 24 (10), 1091 (2008); MG Yasargil, Stuttgart: Georg of Manipulative and Physiological therapeutics 7 (4), 261 (1984); BGH Thieme Verlag 119 (1969). Lamberty and S �ivanovi�, Cells Tissues Organs 85 (1), 113 (1973); J 8. Eduardo Seoane and Albert L Rhoton, Surgical neurology 51 (5), 500 Mitchell, Cells Tissues Organs 163 (2), 113 (1998); C Taitz and H Nathan, (1999). Cells Tissues Organs 127 (3), 212 (1986). 9. Müge Sandikçioğlu, SØren Skov, and Beni Solow, The European Journal of Orthodontics 16 (2), 96 (1994). 10. Jarostaw Wysocki, Mariusz Bubrowski, Jerzy Reymond, and Jan Kwiatkowski, Folia Morphologica-Warszawa-English Edition 62 (4), 357 (2003). 11. Robert Wayne Bailey, The cervical spine. (Lea & Febiger, 1974). 12. Qudusia Sultana, Ramakrishna Avadhani, KL Varalakshmi, and MH Shariff, Nitte University Journal of Health Science 5 (2) (2015). 13. N Vasudeva and R Kumar, Cells Tissues Organs 152 (3), 230 (1995). 14. R Shane Tubbs, Philip C Johnson, Mohammadali M Shoja, Marios Loukas, and W Jerry Oakes, Journal of Neurosurgery: Spine 6 (1), 31 (2007). 15. Satheesha Nayak, Venkata Ramana Vollala, and Deepthinath Raghunathan, Neuroanatomy 4, 39 (2005). 16. Satheesha Nayak, Neuroanatomy 6, 28 (2007). 17. RJ Terry and M Trotter, in Morris' human anatomy: a complete systematic treatise (The Blakiston New York, 1953), pp. 288; H Sherk and W Parke, (Philadelphia: JB Lippincott, 1989). 18. Servikal Omurgada Aksesuar Transvers Foramen, Turkish neurosurgery 21 (3), 384 (2011). 19. Divya Agrawal, Biswa Bhusan Mohanty, Sunita Sethy, Bijaylaxmi Parija, Santosh Kumar Hazary, and Prafulla Kumar Chinara, Int J Cur Res 4, 120 (2012); LA Hadley, The American journal of roentgenology, radium therapy, and nuclear medicine 80 (2), 306 (1958); SE Hyyppä, EM Laasonen, and V Halonen, Neuroradiology 7 (1), 49 (1974). 20. AM Levine and CC Edwards, The Orthopedic clinics of North America 17 (1), 31 (1986). 21. John A Gehweiler Jr, Denise E Duff, Salutario Martinez, Michael D Miller,